Recently, the advantages of modeling and fabricating microcavity integrated vacuum tubes are receiving increasing attention by designers of electronic systems. Microcavity integrated vacuum tubes are micrometer-sized devices that employ field emission instead of thermionic emission to generate charge carriers. These vacuum tubes operate as do the conventional vacuum tubes, but are fabricated on a silicon wafer in much the same way as are conventional integrated circuits.
Thin-film methods have been designed to create device layers and microlithography has been used to pattern various layers for these purposes. Conventional methods of producing micro-cavity integrated vacuum tubes, however, use a combination of oxides and refractory metals to form the microcavity structures. There are several problems associated with this approach.
First of all, these process techniques generally use some type of wet-etch process to carve or etch out a cavity within a semiconductor substrate. The wet-etch process is messy and, following the etching, a certain amount of residue is likely to remain. Secondly, during the process, oxide fills the cavity over which a high temperature refractory metal is placed. Once the refractory metal is in place, a wet-etch process is necessary to remove the oxide from within the cavity. Removing the oxide necessitates both a wet-etch technique and the use of refractory or high temperature metals. The wet-etch technique is necessary because of the chemical properties of the oxide. The high temperature or refractory metals are necessary to resist the corrosive effects of the wet-etch techniques. The result of this wet-etch technique often is a less than fully evacuated cavity within the substrate, a partly corroded refractory metal, and the potential of wet-etch residue within the cavity. As a result, less than optimal performance of the microcavity integrated vacuum tube can be expected using this technique.
If a process existed that could avoid the use of refractory metals, oxides for the cavity filling material, and the wet-etch techniques, a significantly improved vacuum micro-chamber would result. The benefits of having a clean vacuum chamber for the production of microcavity integrated vacuum tubes and other electronic devices may, then, be seen in many applications. These applications may include nuclear reactor instrumentation, fusion reactor instrumentation, accelerator instrumentation, bore hole seismic profiling, and space power systems. Additionally, high speed sensors, communication systems, and data processing systems would likely benefit from the high speed that vacuum chamber devices such as vacuum triodes or diodes on an integrated semiconductor substrate could achieve. Consequently, there are both the need for improved processing techniques and a variety of applications for these vacuum microelectronics devices.
In essence, there is a need for a method of producing a vacuum micro-chamber for encapsulating a microelectronics device that avoids the use of oxide as the micro-chamber spacer material.
There is the need for a method of producing a vacuum micro-chamber device that permits the use of lower temperature metals such as copper, aluminum, and their alloys and, thereby, takes advantage of their manufacturing properties.
There is a further need for a method of producing a vacuum micro-chamber for encapsulating a microelectronics device that fully avoids the use of wet-etch techniques that leave residues and may not fully evacuate the vacuum micro-chamber of the chamber spacer material.